Thermoplastic polymers are widely employed to create a variety of products, including blown and cast films, extruded sheets, foams, fibers and products made therefrom, woven and knitted fabrics, and non-woven fibrous webs. Traditionally, many of these articles have been made from petroleum-based thermoplastics such as polyolefins.
There is a growing interest in replacing these petroleum based polymers with resource renewable polymers, i.e. polymers derived from plant based materials. Ideal resource renewable polymers are “carbon dioxide neutral” meaning that as much carbon dioxide is consumed in growing the plant based material as is given off when the product is made and disposed of. Biodegradable materials have adequate properties to permit them to break down when exposed to conditions which lead to composting. Examples of materials thought to be biodegradable include aliphatic polyesters such as poly(lactic acid), poly(glycolic acid), poly(caprolactone), copolymers of lactide and glycolide, poly(ethylene succinate), polybutylene succinate), polyhydroxybutyrate, and combinations thereof.
Degradation of aliphatic polyesters can occur through multiple mechanisms including hydrolysis, transesterification, chain scission, and the like. Instability of such polymers during processing can occur at elevated temperatures as described in WO 94/07941 (Gruber et al.).
The processing of aliphatic polyesters as microfibers has been described in U.S. Pat. No. 6,645,618. U.S. Pat. No. 6,111,160 (Gruber et al.) discloses the use of melt stable polylactides to form nonwoven articles via melt blown and spunbound processes.
Many thermoplastic polymers used in these products, such as polyhydroxyalkanoates (PHA), are inherently hydrophobic. That is, as a woven, knit, or nonwoven such as a spunbond fabric, they will not absorb water. There are a number of uses for thermoplastic polymers where their hydrophobic nature either limits their use or requires some effort to modify the surface of the shaped articles made therefrom. For example, polylactic acid has been reported to be used in the manufacture of nonwoven webs that are employed in the construction of absorbent articles such as diapers, feminine care products, and personal incontinence products (U.S. Pat. No. 5,910,368). These materials were rendered hydrophilic through the use of a post treatment topical application of a silicone copolyol surfactant. Such surfactants are not thermally stable and can break down in an extruder to yield formaldehyde.
U.S. Pat. No. 7,623,339 discloses a polyolefin resin rendered antimicrobial and hydrophilic using a combination of fatty acid monoglycerides and enhancer(s).
Coating methods to provide a hydrophilic surface are known, but also have some limitations. First of all, the extra step required in coating preparation is expensive and time consuming. Many of the solvents used for coating are flammable liquids or have exposure limits that require special production facilities. The quantity of surfactant can also be limited by the solubility of the surfactant in the coating solvent and the thickness of the coating.
Post treatment of the thermoplastic polymer can be undesirable for at least two other reasons. First, it can be more expensive since it requires additional processing steps of surfactant application and drying. Second, PHAs are polyesters, and thus prone to hydrolysis. It is desirable to limit the exposure of PHA polymers to water which can be present in the surfactant application solution. Furthermore, the subsequent drying step at elevated temperature in the wet web is highly undesirable.